Interest in fuel cell batteries as power sources for portable electronic devices has grown. A fuel cell is an electrochemical cell that uses materials from outside the cell as the active materials for the positive and negative electrodes. Because a fuel cell does not have to contain all of the active materials used to generate electricity, the fuel cell can be made with a small volume relative to the amount of electrical energy produced compared to other types of batteries.
Fuel cells can be categorized according to the type of electrolyte used, typically one of five types: proton exchange membrane fuel cell (PEMFC), alkaline fuel cell (AFC), phosphoric-acid fuel cell (PAFC), solid oxide fuel cell (SOFC) and molten carbonate fuel cell (MCFC). Each of these types of fuel cell can use hydrogen and oxygen as the active materials of the fuel cell negative electrode (anode) and positive electrode (cathode), respectively. Hydrogen is oxidized at the negative electrode, and oxygen is reduced at the positive electrode. Ions pass through an electrically nonconductive, ion permeable separator and electrons pass through an external circuit to provide an electric current.
In some types of hydrogen fuel cells, hydrogen is formed from a hydrogen-containing fuel supplied to the negative electrode side of the fuel cell. In other types of hydrogen fuel cells, hydrogen gas is supplied to the fuel cell from a source outside the fuel cell.
A fuel cell system can include a fuel cell battery, including one or more fuel cells (such as a fuel cell stack), and a hydrogen source, such as a fuel tank, a hydrogen tank or a hydrogen gas generator. Gas generators that supply gas to a fuel cell can be an integral part of the fuel cell system, they can be removably coupled to the fuel cell system, or they can include replaceable components containing reactants. A removable gas generator can be replaced with another one when the gas producing reactants have been consumed. Removable gas generators can be disposable (intended for only a one-time use) or refillable (intended for use multiple times) to replace consumed reactant materials.
Hydrogen generators can provide hydrogen from a variety of hydrogen containing materials and a variety of methods for initiating the release of hydrogen. Examples of hydrogen containing materials include liquid or gaseous hydrocarbons (such as methanol), hydrides (such as metal hydrides and chemical hydrides), alkali metal silicides, metal/silica gels, water, alcohols, dilute acids and organic fuels (such as N-ethylcarbazon and perhydrofluorene). A hydrogen containing compound can react with another reactant to produce hydrogen gas when the reactants are mixed together, in the presence of a catalyst, heat or an acid, or a combination thereof.
In selecting reactants for use in a hydrogen generator, consideration may be given to the following: (a) stability during long periods of time when the hydrogen generator is not in use, (b) ease of initiation of hydrogen release (c) the amount of energy that must be provided to sustain the release of hydrogen, (d) the maximum operating temperature, and (e) the total volume of hydrogen that can be produced per unit of volume and per unit of mass of thehydrogen-containing material(s).
Some hydrogen containing materials can be heated to evolve hydrogen in a chemical decomposition reaction. A hydrogen generator using such types of materials can be advantageous with regard to the volume of hydrogen that can be produced compared to other types of hydrogen generators, such as those with a liquid reactant.
An object of the present invention is to provide a hydrogen generator with one or more of the following features: a self-contained assembly including all necessary elements contained within a structure that is easily incorporated into a fuel cell system and/or which serves as a fungible fuel source therefor; an assembly which only selectively generates hydrogen; and an assembly which accommodates and segregates the reaction byproducts within a unitary reaction chamber.